This invention relates to an apparatus and method for heating or thermally stretching bolts, and more particularly to such an apparatus and method for heating hollow bolts while the bolts are operably mounted to enable their proper installation or removal.
Heretofore, it has been common practice, when using conventional helically threaded bolting means for fixedly securing mating flanges or portions of members to be connected, to thermally stretch or elongate the hollow bolts prior to rotatably tightening the associated conventional nut means to provide a predetermined tension preload while minimizing the application of rotational force to the nuts. In releasing such made up bolting means, the thermal stretch or elongation is also employed so the bolting means will grow or lengthen sufficiently to enable the associated nut means to be rotatably loosened with less force. In order to heat the bolts in a minimum of time, the bolts have been provided heretofore with internal bores and suitable heating means have been inserted within the internal bore for heating the bolts.
Referring, for example, to U.S. Pat. No. 2,176,601 dated Oct. 17, 1939 an electrical resistance heating element is inserted within the internal bore of a bolt to heat the bolt with the bolt forming a part of the electrical circuit. Also, U.S. Pat. No. 1,682,338 dated Aug. 28, 1928, and U.S. Pat. No. 2,359,046 dated Sept. 26, 1944, both disclose a heating element inserted within a bore in a bolt for heating the bolt prior to tightening the nut onto the bolt. In general, electrical heating is slow and requires an excessive amount of time to tighten or loosen the plurality of bolt means employed to secure an item of equipment.
In U.S. Pat. No. 2,320,398 dated Jun. 1, 1943, an arrangement is shown for cooling bolts after being heated by the circulation of a cooling fluid or medium about the bolts. However, there is no suggestion of using a circulating fluid for heating the bolts prior to tightening of nuts thereon.